1. Field of the Invention
The present invention relates generally to servo control systems used for positioning read/write transducers in data storage devices, and more particularly, to providing a re-read of data read prior to a read inhibit for data recovery and validation in a sampled position data storage device.
2. Description of Related Art
It is well known in the art to store data on magnetic or optical disk drives. Data is stored on a disk drive on one or more tracks of predetermined format disposed on a disk-shaped recording media. The data is written to and read from the tracks using one or more transducers, which typically comprise read/write heads. Reading data from a desired one of the tracks on the disk surfaces requires knowledge of the read/write head position relative to the track as the disk rotates and the head is moved across the disk, and requires precise centering of the head over the disk track. Conventionally, the read/write head is mounted on a head positioning assembly that is moved by a servo control loop.
The servo control loop controls movement of the head positioning assembly across the disk surface to move the read/write head from track to track (track seeking) and, once over a selected track, to maintain the read/write head in a path over the centerline of the track (track following). Centering the read/write head over a track permits accurate reading and recording of data in the track.
In most devices, the servo control loop is a closed loop system that utilizes sampled position information, also known as servo information, obtained from the disk surface to provide feedback for the track seeking and track following functions. Some devices store this position information between the data regions of the disk surface (known as an embedded servo system).
The sampled position information usually includes: a synchronization field, such as for automatic gain control (AGC) or similar signal detecting purposes; a track identification (TID) field typically comprising a digitally encoded Grey code; and a position error signal (PES) field generally containing one or more burst patterns. The PES, which is proportional to the relative difference of the positions of the center of the read/write head and the nearest track centerline, is a corrective signal providing an indication of which direction the head should be moved to during either track seeking or track following functions.
As the track densities of disk drives increase, the accuracy of the PES becomes increasingly important. Unfortunately, as track pitch decreases, the tolerances arising in the manufacture of the read/write heads do not decrease proportionately, and this results in heads that either write or read more narrowly relative to track pitch. This narrow read or write characteristic results in more xe2x80x9csoftxe2x80x9d and xe2x80x9chardxe2x80x9d errors resulting from misregistration of the read/write heads.
To minimize the limitations in the prior art described above, and to minimize other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a data storage device that performs a re-read of data read prior to a read inhibit for data recovery and validation. When misregistration of read/write heads occurs, as indicated by a sampled servo position, data read from a track of the data storage device is withheld from a host until a subsequent sampled servo position is verified to be within a read limit width of the track. Data blocks read preceding the servo position that caused the posting of the read inhibit are re-read, once the read inhibit is cleared. If the read inhibit is not present following the re-read of the data, this re-read data can be released to the host